The present invention relates to inducers, and more particularly to inducers having shrouded rotors.
Inducers are commonly used to pressurize fluid. Generally, inducers comprise a rotor rotatably mounted in a static housing. The rotor includes a hub and a plurality of blades extending outward from the hub. Conventional inducers operate at relatively low operating speeds (i.e., the rotor rotates at relatively low speeds in the housing). At intermediate speeds, blade erosion commonly occurs due to cavitation of fluid against the blades and flow separation near the blade tips.
One solution to the erosion problem is to operate inducers at lower operating speeds, i.e., below an empirical blade erosion-free speed. For example, operating speeds of about 152 m/s (i.e., about 500 ft/s) in a liquid oxygen (LOX) environment have been common. The lower operating speeds result in lower performance levels, and thus more impeller stages are required in a pressurizing system. For example, instead of requiring one inducer, or a few inducers in series to accomplish a desired total pressure increase, many more inducers are required. Cost and complexity increase with the number of inducers.
Another solution for the blade erosion and failure problem, often used in combination with the lowering speed solution, is to provide a circumferential shroud extending between each adjacent pair of blades. These conventional shrouds have a constant thickness around the circumference of the shroud. However, adding such a shroud greatly increases pump weight and cost.
Though the typical inducer shroud alleviates the erosion problem, structural problems can occur at higher speeds. For example, shrouds may deform radially to such an extent that they rub against the inducer housing. Alternatively, more clearance may be left between the shroud and the inducer housing, but this reduces pump efficiency. These problems necessitate operation of inducers at lower speeds, which causes poor performance.